Process of casting plastic sheeting



, continuous.

. Patented Mar. 10, 1942 P BOCESS OF CASTING PLASTIC SHEETING Gustave B.Bachman, Lafayette, Ind., and Carl N. Behrndt, Rochester, N. Y.,assignors to Eastman Kodak Company, Rochester, N. Y., a corporation ofNew Jersey No Drawing. Application September 15, 1939, Serial No.295,088

3 Claims. (Cl. 106-181) This invention relates to the casting ofsheeting from plastics, such, for instance, as cellulose esters,methacrylate resins, polyvinyl acetal resins, polyvinyl acetate, orbutyl resinic lactone. The preparation of butyl resinic lactone isdescribed in the copending application of J. G. McNally and R. H. VanDyke, Serial No. 248,496. The casting of sheeting, such as photographicfilm base, wrapping tissues, etc., from plastics, such, for instance, ascellulose esters, is well known. A solution of plastic and plasticizer,in a volatile solvent or solvent mixture, is spread in a thin, uniformlayer on a, highly polished the dope by adding it to the plastic duringthe surface, and the solvent allowed to evaporate.

In the most common form of casting, the plastic solution or "dope isspreadon a nickel or chromium-plated surface which forms the peripheryof a rotating wheel, so that the casting process is The wheel is oflarge diameter, so that by the time the wheel has made approximately,three-fourths of a rotation after the spreading of the dope on itssurface, the solvent has evaporated to a sufficient extent to set theresulting film and permit of stripping it from the casting surface. Acertain amount of tension is usually necessary to strip the film fromthe casting surface. In some cases the tension required is so severethat the film is damaged in stripping, small pieces being pulled fromthe surface of the film, or the film being torn.

We have discovered that the stripping of plastic sheeting from thecasting surface may be facilitated, so that littleor no tensionisrequired to strip it, by incorporating in the surface of the sheetingadjacent to the casting surface a dialkyl ester of sulfosuccinic acid,either in its free form or in the form of an alkali metal salt, e. g.the sodium salt. The dialkyl esters of sulfosuccinic acid, and theirsalts, are described in U. 8. Patent 2,028,091. For example, the diamyl,dihexyl,

I paringthe solution of sulfosuccinic acid dialkyl ester, or its salt,may be acetone, methanol, or any other volatile solvent for thesulfosuccinic acid ester which is not injurious to the plastic solutionor dope. A 4% solution of sulfosuccinic 55 "ester of sulfosuccinicacid,"

acid ester may suitably be used. This percentage is illustrative only,and we are not to be limited thereby.

When the dialkyl ester of sulfosuccinic acid, or its salt, isincorporated in the plasticsolution or dope, we may use from 0.05% to5%, approximately. of the sulfosuccinic acid ester, calculated on theweight of the plastic (cellulose ester or resin).

Instead of adding the sulfosuccinic acid ester directly to the dope, wemay incorporate it in preparation of the plastic. For instance, in thecase of cellulose acetate, it may be introduced during acetylation orpretreatment, or in a wash previous to, or following, acetylation. Inthe case of polymeric resins, it may be added just prior to or duringthe polymerization.

Mixtures of any of the dialkyl esters of 'sulfosuccinic acid, or theirsalts, in any desired proportions, may, of course,;be used.

Incorporation of a salt of a dialkyl ester of sulfosuccinic acid into aplastic dope has an additional beneficial effect in certain cases.Partially hydrolyzed lower fatty acid esters of cellulose, particularlythe esters of wood pulp cellulose, often exhibit an inflated viscosityin organic solvents, such as dry acetone, which is believed to be due tothe ash content of the esters as explained in U. S. Patent No. 2,126,489of Malm. The proportion of mineral salt, particularly of calcium saltcausing this "salt effect may be (and usually is in a well washedproduct) only a small fraction of one percent based on the celluloseester, such as would be imparted by washing the cellulose ester innatural water instead of salt-free water. We have found that by theincorporation of 0.1% to 5% of a salt of a dialkyl ester ofsulfosuccinic acid into such a cellulose ester dope or solution, theviscosity is reduced, the amount of this reduction beingproportional tothe salt effect which had been exerted upon the cellulose'ester.

This power ofl'cancelling the effect of mineral salts is also possessedby the salts of the alkyl substituted aromatic sulfonic acids, such asare stated to be useful as antiherents in the copendmg application of c.J. Stand and can. Bachman, SerialNo. 231,916, filed September 27, 1938.The alkyl substituted aromatic sulfonic acids and their salts may alsobe applied, in solution, to the casting wheel for facilitating stripp'ne of plastic films, as well as incorporated in the dope.

In the appended claims. by the term dialkyl we mean to include not onlythe tree esters, but their alkali metal salts.

be secured by Letters Patent of the United States is.

a plasticizer, and a diaikyi ester of sulfosuccinic acid.

2. A solution. in a volatile organic-solvent, of

a cellulose ester and a plasticizer, adapted to be 10 What we claim asour invention and desire to 1. A composition comprising a celluloseester,

- cast on a casting surface to form transoarent sheeting, containing, asa. substance for facilitating stripping of the sheeting from the castingsurface, from 0.05% to 5% of a dia1kyl ester of sultosuccinic acid.

3. A transparent sheet comprising a cellulose ester, a plasticizer, anda dialkylester oi. sulfosuocinic acid.

GUSTAVE B. BACHMAN; CARL N. BEHRND'I.

